The invention relates to an open-end friction spinning machine having at least one friction surface assigned to a suction device which is connected to an underpressure or vacuum source via a valve that regulates the magnitude of the suction effect and the switching off of the suction device.
In a known apparatus of the above-mentioned type described in commonly owned U.S. Pat. No. 4,522,023 issued June 11, 1985, the friction surface is configured as a wedge-shaped gap between two adjacently arranged rollers. At least one of the two rollers exhibits a perforated cover surface containing a suction pipe of a suction device inside. This suction device is connected to an underpressure or vacuum source by means of a blocking and controlling valve allowing the switching on and switching off of the suction effect of the suction device. In practice difficulties were recognized in designing and operating a blocking and control valve in such a manner, that after the suction effect of the suction device was shut off and again resumed, it is exactly the same as before. Thereby it has to also be recognized that many such open-end friction spinning units are combined to form a single machine whereby each of these open-end friction spinning units may exhibit a slightly different setting of the suction effect.
The invention is based on the objective to so develop an apparatus of the above-mentioned type wherein the valve is selectively operable so as to again obtain the exact same suction effect as the prior setting.
This objective is achieved according to the present invention by providing individually operable adjusting means for switching off and for adjusting the suction effect of the suction device at a respective spinning unit.
With the arrangement of the present invention, the suction effect of the suction device usually regulated in very tight tolerances does not change whenever the suction device is shut off, for example, during a yarn breakage and a subsequent piecing process. The setting of the valve does not change during this process.
In a further development of certain preferred embodiments of the invention, it is provided that the adjusting means for switching off the suction effect in the suction device includes an actuator controllable by a yarn breakage guard. It is thereby achieved that during a yarn breakage, the suction effect is automatically interrupted and the friction effect at the friction surface is immediately reduced. Any fiber residues that could possibly remain, are easily removed during a cleaning process. In an advantageous development of certain preferred embodiments, a return or reset element of a movable servicing apparatus for switching on the suction effect is assigned to the actuator of the adjusting means that switches off the suction effect of the suction device. This moveable servicing apparatus automatically attends to again switching on the suction effect at the appropriate time period during the piecing process.
In a further development of certain preferred embodiments of the invention, it is provided that the adjusting means of the valve includes an adjustable stop for limiting the movement of a valve body towards its opening position. This stop, that is not changed during the switching off of the suction effect, determines the suction for the normal operational condition. In an advantageous further development, a moveable servicing apparatus is provided which includes means for regulating the adjustable stop. The precise setting of the suction effect desired for the normal operational condition is then performed by the servicing apparatus. The normal operational condition is not changed each time the operation is interrupted and the suction effect discontinued, which means that the suction effect is again precisely the same after an interruption in the operation.
In an advantageous embodiment of the invention, the valve is configured as a flap or leaf valve arranged with the flap or leaf on a shaft and the adjusting means engaging at the shaft of the flap or leaf. This results in a simple, but at the same time also, precise adjustment mechanism. In an advantageous further development a radially directed counter stop is attached at the shaft that corresponds with the adjustable stop limiting the opening position. Furthermore, it is advantageous if the shaft is connected to a spring loading the same in the opening direction of the valve and retaining same in said opening position determined by the stop, wherein the closing movement of the valve for switching off the suction effect occurs against the effect of the spring. This results in a very simple but very precise mechanism permitting a fast switching off of the suction effect of the suction device as well as a fast re-activation of the suction effect to the pre-existing value.
In a further development of preferred embodiments of the invention, at least one cleaning device connectable to the underpressure or vacuum source of the suction device via a valve is provided having adjusting means that are controlled in such a manner that simultaneously with the switching off of the suction effect of the suction device, the cleaning device is switched off.